The present invention relates to gyroscopic gimbal assemblies and pertains particularly to methods and apparatus for assembling gimbals.
Conventional production factory assembly of a typical two axis gimbal involves a highly repetitive assembly procedure that takes in excess of two hours. This method is not only extremely time consuming but produces a less than superior assembly. The standard procedure of assembly utilizes a selection fit and the use of a plurality of shims for making relative adjustments in the interdependent parameters of the gimbal assembly.
The axis of intersection of the spin bearing bore and outer gimbal bearing must intersect within 0.0004 TIR to minimize gyro drift due to missile acceleration. The spin bearing bore must also be coincident with the gimbal post bore longitudinal axis within 0.0008 TIR to ensure proper gyro-optics/detector alignment. These alignments of the axes of coincidence and intersection are achieved in a conventional assembly technique by shimming the inner and outer gimbal rings into position.
Another parameter which must be adjusted during assembly is yield, which refers to the magnitude of gimbal compliance along each of the two orthogonal gimbal axes and is measured in microinches of deflection per pound of applied load. A gimbal yield of about 100 microinches per inch pound will result in a gimbal assembly with no free play and smooth gimbal motion under an applied torque. Shims are added or subtracted from beneath the gimbal bearings inner races to increase or decrease the bearing load when the gimbal screw torque is applied to preload the bearing.
Ideally, shims should be removed or added equally to both sides of the gimbal ring during this process, thereby adjusting yield but not axis of intersection. This is not possible because of shim width and flatness tolerances, which results in an interactive assembly process which trades axis of intersection for yield until an acceptable value of each is obtained. This assembly process is extremely time consuming requiring from two to four hours per gimbal assembly.
It is therefore desirable to have an assembly technique which will reduce gimbal assembly time and obtain more reliable accurate parameter adjustment.